Hazards due to UV radiation for human eyes have been suspected and studied for long time. For example, document U.S. Pat. No. 5,949,535 contains a presentation of some of the damages which may be caused by UV radiation upon the eye. In everyday life, most of the UV radiation encountered originates from the Sun, although some of the existing artificial light sources also produce significant amounts of UV radiation.
It is also known that eyewear can provide protection against UV hazard to a wearer. For example, the already-mentioned document U.S. Pat. No. 5,949,535 discloses rating an eyewear according to its solar radiation protection capabilities, in particular in the UV range. Then a user of the eyewear can be informed about its protection efficiency against UV hazard by providing him with a numeral value which quantifies this protection efficiency. The rating method disclosed in this prior art document is based on at least two of the following values: a first transmission value for each eyeglass in the UV wavelength range from 280 nm (nanometer) to 400 nm, a second transmission value for each eyeglass in the blue wavelength range from 400 nm to 500 nm, and a further value for quantifying the amount of incident light that reaches the eye from around the frame which holds the eyeglass on the wearer's face. More precisely, this latter value represents the extraneous light that reaches the eye without being filtered through the eyeglass or absorbed or reflected by the eyewear frame.
But this known rating method does not quantify appropriately in all circumstances the total UV radiation amount which enters into the eye of the eyewear wearer. In particular, there exists some conditions where significant amount of radiation enters into the eye but without being taken into account by this method.
Therefore, an object of the present invention is to provide rating of an eyeglass that quantifies more significantly the protection against UV hazard which is produced by the eyeglass. In particular, the rating should take into account most of the actual conditions of UV eye exposure which occur actually.
Another object of the present invention is to provide a value for rating an eyeglass with respect to UV protection, which can be understood easily and directly by a customer intending to acquire the eyeglass.
Still another object of the invention is to provide a rating value for an eyeglass with respect to UV protection, which can be determined easily, in particular by measuring and/or calculating appropriate optical values.